Transcription factors of the nuclear factor κB (NF-κB)/Rel family play a pivotal role in inflammatory and immune responses (1,2). There are five family members in mammals: RelA, c-Rel, RelB, NF-κB1 (p105/p50), and NF-κB2 (p100/p52). Both p105 and p100 are proteolytically processed by the proteasome to produce p50 and p52, respectively. Rel proteins bind p50 and p52 to form dimeric complexes that bind DNA and regulate transcription. In unstimulated cells, NF-κB is sequestered in the cytoplasm by IκB inhibitory proteins (3-5). NF-κB-activating agents can induce the phosphorylation of IκB proteins, targeting them for rapid degradation through the ubiquitin-proteasome pathway and releasing NF-κB to enter the nucleus where it regulates gene expression (6-8). NIK and IKKα (IKK1) regulate the phosphorylation and processing of NF-κB2 (p100) to produce p52, which translocates to the nucleus (9-11).

RelA/p65 is a subunit of the NF-κB transcription complex, which plays a crucial role in inflammatory and immune responses. The complex is composed of various homodimeric and heterodimeric Rel family member combinations, the activity of which is modulated by post-translational modifications including phosphorylation and acetylation. p65 phosphorylation by PKA and/or MSK1 at Ser276 allows for increased interaction with the transcriptional coactivator p300/CBP to enhance transcriptional activity. NF-κB dimer assembly with IκB, as well as its DNA binding and transcriptional activities, are regulated by p300/CBP acetyltransferases that principally target Lys218, Lys221 and Lys310 (12-14). This process is reciprocally regulated by histone deacetylases (HDACs); several HDAC inhibitors have been shown to activate NF-κB (12-14). T-cell co-stimulation and Calyculin A have both been shown to increase Ser468 phosphorylation (15,16). IKKβ (but not IKKα) and GSK-3β both target this site (16,17), which appears to have a negative regulatory role not involving inhibition of nuclear translocation after TNF-α or IL-1β stimulation (17). p65 phosphorylation at Ser536 regulates activation, nuclear localization, protein-protein interactions, transcriptional activity, and apoptosis (18-22).